Boko Haram will "sell your girls in the market", the terrorist leader has vowed in a chilling video message to parents of the kidnapped Nigerian schoolgirls.

Abubakar Shekau, the leader of the Nigerian Islamist group notorious for targeting schools, claimed responsibility for the abduction of hundreds of girls aged 16 to 18 from their Borno state school in a video message released by Agence France Press.

It is three weeks since the girls were abducted and Boko Haram has threatened to 'sell' them

But a different source, involved in the hostage negotiations, told Channel 4 News that he believes the girls will be returned safely for a ransom. "It would not be hard to engineer a deal. It looks like they want to release them," he said.

As anger swells in Nigeria over the handling of the case, and protest marches take place across the nation, police arrested the leader of a group that called on authorities to do more to find the kidnapped girls.

Reuters reported that Naomi Mutah Nyadar had been detained, suspected of falsely claiming that one of the abducted girls was her daughter.

But local reports suggest the arrest was connected with a meeting with Nigeria's First Lady Patience Jonathan, who had felt slighted that the mothers of the girls did not come to meet her, and were instead represented by Mutah Nyadar, who is from the girls' local Chibok community.

AP quoted community leader, Saratu Angus Ndirpaya, as saying that Jonathan accused the activists of fabricating the abductions in order to smear her husband's government.

Protests for the missing Nigeria schoolgirls

Protests for the missing Nigeria schoolgirls

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Fidelis Olubukola, a member of the Civil Society, Women Advocate Research and Documentation Centre, chants slogans for the release of the schoolgirls kidnapped by Boko Haram more than two weeks ago during a workers' rally in Lagos on May 1, 2014. The mass kidnapping in the Chibok area of northeastern Borno state was one of the most shocking attacks in Boko Haram's five-year extremist uprising, which has killed thousands across the north and centre of the country. AFP PHOTO/PIUS UTOMI EKPEI (Photo credit should read PIUS UTOMI EKPEI/AFP/Getty Images)